TGSL Experiments

[6666]

Just wondering about anti static bag material that IC's come in
just tested some, does not seem to have a dc resistance
but seems to dissipate static ok

[der_fisherman]

Just wondering about anti static bag material that IC's come in
just tested some, does not seem to have a dc resistance
but seems to dissipate static ok

I know the bags, but have none at this time. And you found absolutely no continuity at all? Did you pierce the bag with both probes? If still no continuity, it will be difficult to connect to ground I feel.
Still great thinking outside the box!!
regards
Andy

[simonbaker]

I know the bags, but have none at this time. And you found absolutely no continuity at all? Did you pierce the bag with both probes? If still no continuity, it will be difficult to connect to ground I feel.
Still great thinking outside the box!!
regards
Andy

You can also buy anti-static paint, with similar very high resistance, which I considered -- but people talked me out of it. However, maybe such material has its place. Worth revisiting.

-SB

[6666]

Did you pierce the bag with both probes

Yes, but no DC continuity even on 40meg scale

[der_fisherman]

Yes, but no DC continuity even on 40meg scale

Even with piecing?

[woodbob123]

This may be a little basic I've yet to finish a coil that works well, but does the distance shield is away from the coil have any bearing on how well it works, all the ones I've seen have the shield wraped tight on the windings this gives a thinner coil but not worried about that, may not work with a DD, hard to get a good null but a concentric should be ok. Would the depth gain be greater than the loss caused by coil being further from ground. If there were a gain would it be possible to add a shield on the outside of a finished coil as far away from coil as possible, will be trying this on a surf PI that I have just finished either foil or mylar and a covering of fiberglass tape

[golfnut]

I've yet to finish a coil that works well, but does the distance shield is away from the coil have any bearing on how well it works, all the ones I've seen have the shield wraped tight on the windings this gives a thinner coil but not worried about that, may not work with a DD, hard to get a good null but a concentric should be ok. Would the depth gain be greater than the loss caused by coil being further from ground. If there were a gain would it be possible to add a shield on the outside of a finished coil as far away from coil as possible

I've yet to finish a coil that works well,
- What did you test your coil on?

but does the distance shield is away from the coil have any bearing on how well it works
- I read a guys view that the sheild picks up signal from the coil and radiates it. ie the sheild looks like a dipole - fed from within.

If this is the case - then in the limit, if the distance from coil to inner of shield was massive, then I dont think it would work.

commercial loops (used for direction finding) have no real gap between the turns and the sheild tube - all the turns are rammed in there.

I would guess that if the insulation from the coil to the sheild was thick and was a lossy dielectric material this may loose a fraction of available signal.

There is a good DD article on the silverdog site - I made one and it was good.

Steve

[der_fisherman]

I've yet to finish a coil that works well,
- What did you test your coil on?

but does the distance shield is away from the coil have any bearing on how well it works
- I read a guys view that the sheild picks up signal from the coil and radiates it. ie the sheild looks like a dipole - fed from within.

If this is the case - then in the limit, if the distance from coil to inner of shield was massive, then I dont think it would work.

commercial loops (used for direction finding) have no real gap between the turns and the sheild tube - all the turns are rammed in there.

I would guess that if the insulation from the coil to the sheild was thick and was a lossy dielectric material this may loose a fraction of available signal.

There is a good DD article on the silverdog site - I made one and it was good.

Steve

Dear Steve,
That was a very interesting post from you Steve, then it sounds as though Mylar, insulating side to the coil, will probably be the absolute best material to work with.....which substantiates Don B's feelings for the coils he has built.......
Do you have any further thoughts on the subject of ONLY screening the Rx coil? I don't think that anyone has tested it out yet, or better said, not to my knowledge, but it has been discussed. I would love to hear of your ideas in that area.
many thanks
Andy

[woodbob123]

Sorry did'nt explain myself very well should have read goes together well or looks right to me rather than works well, building igsl,vdi,coil and boxing it up all at the same time. Over weekend saw the inside of a crossfire concentric coil shielding was just two round sheets one each side with springs between them could not test as we were in a pub, will next week. I assume material was of high resistance but could not see shielding on sides but that could have been the beer they may have met My thought was is it neccessary to have shielding as close as we use it, if the main reason is to reduce ground capacitance and reduce interferance will 10mm gap between coil and shield cause any problems. Idealy i would like to use a single sided pcb sheet possibly etched as outer parts of coil or a layer of mylar under final covering. Will do a test on mono coil for surf first. Steve thanks for offer will send a test coil will then be able to believe my test equipment.

[simonbaker]

This may be a little basic I've yet to finish a coil that works well, but does the distance shield is away from the coil have any bearing on how well it works, all the ones I've seen have the shield wraped tight on the windings this gives a thinner coil but not worried about that, may not work with a DD, hard to get a good null but a concentric should be ok. Would the depth gain be greater than the loss caused by coil being further from ground. If there were a gain would it be possible to add a shield on the outside of a finished coil as far away from coil as possible, will be trying this on a surf PI that I have just finished either foil or mylar and a covering of fiberglass tape

I have wondered also if some padding between the shield and coils is beneficial, based on the idea that field lines are strongest right at the windings surface, and we want to reduce interaction of our shields with our TX, RX coils.

It is just so darn difficult to do really good comparison tests for high-sensitivity parameters such as depth. As Don said, you'd want to use the same coils and change the shields to compare, which is hard to do realistically (meaning a completed, potted coil assembly), although worth trying in some form. Using different coils is really not easy because people on these forums have found great differences (often mysterious) between coils they built.

-SB

[6666]

Even with piecing?

Yes

[Dennis the Mennis]

1. Did I notice something funny with the voltage at C15 as the signal continued to increase -- did the C15 voltage reverse near the maximum null voltage?

I'll have to check again , can't tell anymore which position it was .
When posting my clip I was allready busy wrapping the AL foil around my testcoils ...

2. I also am very interested in your large increase of noise at the LM308 output when the RX signal moves away from the null point.

Isn't it due to the different voltage settings for the FET's ... I don't know what happens.
I thought this ( the increase of noise ) was normal behaviour but I guess not ...
Did I find another succesfull way in the wrong direction ?


I don't understand it. My current thought is that it is not really EMI noise but possibly mechanical vibration that is amplified because the vibration modulates a larger residual null signal. Probably wrong. The other possibility is that the noise is some kind of jitter or modulation of the TX signal that is coupled more strongly when off-null.

What else could it be? I don't see why EMI noise would increase.

I told you that this all happens within the millimeter .Perhaps I have the (dis)advantage with this scope making this visible.
Due to the very long timebase there is a momentary peak while trying to slide the coils .
Must say that the average noise can be higher .

What I can't understand is that your noise is about the same at almost any coil overlap ...
Allthough I have the old TGS pcb it should work properly , and have the idea it does .
Both coils are firmly glued and the only vibration would take place during sliding the coils ( the peak ..?) in the shielding .
So some more experimenting to do

Can you try separating the coils completely and tilting them so they are minimum coupled, and check the LM308 output noise?

Regards,

-SB

P.S. I just tried the same null vs noise test on my setup (using a dfbowers PCB and unshielded coils, USB cable). My coils are mounted to plexiglass plates in my "nulling machine" as shown in a previous photo.

I did not get an increase in noise at LM308 output when I changed the coil overlap (unlike your test). It remained about the same for all overlaps and RX signal null voltages.

I think I am testing correctly.

Maybe you should try fixing your coils firmly when you move off the null and see if the noise voltage drops back down.

-SB

Kind regards and to be continued ,

Danny

Dennis the Mennis

[simonbaker]

Kind regards and to be continued ,

Danny

Dennis the Mennis

Ok, good to hear. Let us know if you find anything more on the noise.

Regards,

-SB

[simonbaker]

null phase and GB

While my foil shields are on my test coils (dfbowers coils), I repeated the experiments to see if discrimination and ground balancing were sensitive to null phase.

I used a nickel and piece of foil to test discrimination (a penny is not discriminated even at full disc pot setting. If I ground the Rx lead, it seemed that I could slightly disc out the penny, but not sure).

I did not find any affect of the null signal phase on the disc settings as far as I could tell. I used the tone as an indicator of when disc was achieved. A better way might be to use two oscilloscopes, one to watch null phase, the other to watch the output of LM308 and see where the signal inverts due to the disc control.

I used a small ferrite rod to test the GB setting. As far as I could tell, the null phase did not affect where I set the GB setting to ignore the ferrite. I tried both ALL METAL and DISC modes. However, ferrite seems to make a very broken signal as it nears rejection, so the test is very approximate. But the disc control certainly did not track the null phase.

I somehow expected the GB setting to be slightly different depending on which side of the null I was on, but not to change significantly when staying on one side of the null. However, within my margin of error, I could not find a difference even when changing sides. But I think a few degrees is not easy to notice with the pot settings or by ear listening to the tone. I tried to watch the output of the LM308, but it is so low sweep and I don't have a consistent target scanner, so couldn't make conclusions.

Thats it for now.

-SB

[Dennis the Mennis]

Tx and Rx coil separated

Simon asked for an example to completely separate Tx and Rx coils :

Here is a clip of the results , the first clip is made with an cable similar to Belden 8723 ; 2 twisted pairs , each pair shielded separatly and ground wire .

The second clip is made with a Belkin usb cable .


I've started both clips in a kind of start position :

Tried to 'null' the coils as much as possible ( I had a 2 meter extension cable made to the Rx coil ) from there I removed the Rx coil away about 1,5 - 2 meter from the Tx coil.

The extension cable has 2 twisted pairs but only each wire is shielded .

The separation of Tx and Rx is a great way for noise hunting !

It made made me painfull clear that I was operating on the edge of the noise ( the biggest noise source ) : the two laptops on my desktop .

In the test setup I usually do , I will keep the next time a little more distance from my desktop .

The testpoints in the clip are the output LF353 (red) vs the output of the LM308 (green)

I've added two extra measurements in the bottom :

- the peak to peak values for the sample time at that moment ( I've made serveral)
- the max , min and average (noise) frequency for the sample time

So please set the quality in Youtube in 720p HD and Full Screen for max result.

In the end of the first clip I've tried to move the Rx coil a little closer towards my desktop ,so this explains the little more noise at the end ...

Had some difficulties with triggering in second clip ...


1) Belden 8723 (similar cable) http://youtu.be/hgXPTS5e4FQ?hd=1

2) Usb cable (Belkin): http://youtu.be/yrtVT2oSsaw?hd=1


In this example the Usb cable with my pcb ( the old TGS ) seems like an untamed beast ... I don't know why yet

The cables from my pcb to the front controls ( disc pot / sens pot , etc ) are twisted.
Could this cause troubles ?

The more things are closer watched the more questions are raised .......


kind regards

Danny

Dennis the Mennis